Field of the Application
The application generally relates to wireless communications, and more particularly, to relay in Proximity-based Service (ProSe) communication.
Description of the Related Art
With growing demand for ubiquitous computing and networking, various wireless technologies have been developed, including Global System for Mobile communications (GSM) technology, General Packet Radio Service (GPRS) technology, Enhanced Data rates for Global Evolution (EDGE) technology, Wideband Code Division Multiple Access (WCDMA) technology, Code Division Multiple Access 2000 (CDMA-2000) technology, Time Division-Synchronous Code Division Multiple Access (TD-SCDMA) technology, Worldwide Interoperability for Microwave Access (WiMAX) technology, Long Term Evolution (LTE) technology, LTE-Advanced (LTE-A) technology, and Time-Division LTE (TD-LTE) technology, etc. By employing one of the wireless technologies, a mobile communication device (which may be referred to as User Equipment (UE)) may wirelessly connect to a service network for accessing the Internet or obtaining mobile services, including the Proximity-based Service (ProSe), anytime and anywhere. The ProSe represents an enormous recent social-technological trend.
Using LTE technology as an example, the ProSe is first introduced in Release 12 of the 3rd Generation Partnership Project (3GPP) specifications. A ProSe-enabled UE may discover other ProSe-enabled UEs in its vicinity by using only the capabilities of the two UEs or by the assistance of an LTE network. In addition to ProSe discovery, a ProSe-enabled UE may act as a relay between two other ProSe-enabled UEs in its proximity or between a ProSe-enabled UE in its proximity and the LTE network, to provide ProSe communication therebetween. However, according to the 3GPP Technical Report (TR) 23.713, a ProSe-enabled UE which acts as a relay (referred to as a relay UE herein) is first required to connect to an LTE network and request for radio resources for use in ProSe communication, and is also required to always transmit a Device-to-Device (D2D) Synchronization Signal (D2DSS) for allowing another ProSe-enabled UE which is out of service of the LTE network (referred to as a remote UE) to be able to transmit data to the LTE network via the relay UE. As a result, relay UEs may suffer from serious power consumption due to D2DSS transmission. Moreover, the resource utilization of LTE networks may be inefficient since there may be situations where the requested radio resources have been allocated, but there are no remote UE requests to use ProSe communication.